Material Extrusion

First let's start off with the most common and most familiar method of 3D printing: FDM or Fused Deposition Modeling. More or less the hot glue gun method of 3D printing. A spool of filament made of thermoplastic material is fed through a heated nozzle. The nozzle melts the filament while the printer moves the nozzle, depositing the material on a build platform. The material cools and solidifies into a solid object. Once a layer is complete the printer will continue to build layer-upon-layer until the final object is completed.

Vat Polymerization

Next up, we have the two vat methods: Stereolithography (SLA) and Digital Light Processing (DLP). Both utilize a vat of photopolymer resin that is selectively cured by a UV light. The difference being that SLA uses a single laser that draws the model layer while DLP uses a digital light projector to flash a single image of each layer all at once making this process faster than SLA.

Material Jetting

Next on the list we have Material Jetting (MJ) 3D printing methods. MJ works much like the inkjet printer you may have at home. These printers work by depositing layers of photopolymer droplets, instead of ink, which is then cured by a UV light. After one layer has been cured the build platform lowers and another layer is applied. This process repeats until the 3D object is completed. Another method of material jetting is Drop on Demand (DOD) which uses a pair of inkjets, one that deposits the build material and the other is a dissolvable support material.

Cons: Brittle, higher cost than other methods, not good for mechanical features.

Binder Jetting

Binder Jetting 3D Printer Image Source

This process of 3D printing utilizes a powder bed of material (sand or metal) and a liquid bonding agent that selectively bonds areas to create a 3D model. An initial layer of material is spread across the build platform, next a print head moves across the material and applies the binding agent droplets to a specific area to bind the powder together. Once a layer is complete the powder bed is lowered and another layer is applied, this process repeats until the object is completed.

Powder bed fusion produces solid objects using a laser or high energy beam to fuse particles one layer at a time. The process starts with a thin layer of powder spread across a build platform. Next, a thermal source (laser or high energy beam) heats the powder to either fuse or melt a cross-section of the object, once complete the build platform lowers and another layer of powder is spread across so the process can repeat until the object is finished. There is a wide range of powders that can be used, from polymers to precious metals. The most common powder materials are nylon, stainless steel, aluminum, and titanium.

As you can see there are several different methods of 3D printing or as those who are in the industry know it, additive manufacturing. Below is a chart that shows these methods plus a few more. The industry is constantly innovating and discovering new ways to refine and push the limits of 3D printing technology.